Method for minimizing the gap between a rotor and a housing

ABSTRACT

A method for minimizing the gap between a rotor, particularly a rotor vane, and a housing, particularly a housing of a turbine, wherein the gap between rotor and housing is adjustable is provided. The method includes displacing rotor and housing with respect to one another, to provide a simple way of minimizing the gap between rotor and housing. An output signal from a structure-borne sound monitoring system assigned to the rotor and/or housing is taken as a metric for the size of the gap and thus for setting a minimum gap.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2013/064901 filed Jul. 15, 2013, and claims the benefitthereof. The International Application claims the benefit of GermanApplication No. DE 102012213016.0 filed Jul. 25, 2012. All of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a method for minimizing the gap between arotor, especially a rotor blade, and a housing, especially a housing ofa turbine, wherein the gap between rotor and housing can be adjusted,especially by displacement of the rotor and the housing in relation toeach other. It also relates to a turbine, especially a gas turbine,comprising a rotor, especially a rotor blade, and a housing, wherein thegap between rotor and housing can be adjusted by means of an adjustingdevice, especially by displacement of rotor and housing in relation toeach other.

BACKGROUND OF INVENTION

A turbine is a turbomachine which converts the internal energy(enthalpy) of a flowing fluid (liquid or gas) into rotational energy andultimately into the mechanical driving energy. Some of its internalenergy is extracted from the fluid flow by the laminar circumflow—whichis swirl free as far as possible—around the turbine blades, whichportion of internal energy is transferred to the rotor blades of theturbine. Via these rotor blades, the turbine shaft is then made torotate, the useful power being transmitted to a coupled working machine,such as a generator. Rotor blades and shaft are parts of the movablerotor or rotating component of the turbine which is arranged inside ahousing.

As a rule, a plurality of blades are mounted on the shaft. Rotor bladeswhich are mounted in one plane form a blade wheel or rotor wheel in eachcase. The blades are profiled with a slight curve, similar to anaircraft airfoil. A stator wheel is customarily located in front of eachrotor wheel. These stator blades project from the housing into theflowing medium and cause it to swirl. The swirl which is generated inthe stator wheel (kinetic energy) is utilized in the following rotorwheel in order to cause rotation of the shaft upon which the rotor wheelblades are mounted.

Stator wheel and rotor wheel together are referred to as a stage. Aplurality of such stages are frequently connected in series. Since thestator wheel is stationary, its stator blades can be fastened both onthe inside of the housing and on the outside of the housing, andtherefore provide a support for the shaft of the rotor wheel.

A gap, which for example serves for compensation of the heat expansionduring operation, usually exists between the rotor blade tips of therotor and the housing. In order to achieve a high level of efficiency,the gap between blade tip and housing is to be minimal, however, sincefluid flows through the gap past the rotor blades and therefore does notcontribute to energy generation.

Contingent upon the conical shape of the turbine and of the housingenclosing it, it is possible to influence the gap size by a displacementof the rotor in relation to the housing by means of a correspondingadjusting device. Methods for displacement of rotor relative to thehousing are known from DE 42 23 495 and WO 00/28190, for example.Methods for gap minimization are known from DE 39 10 319 C2, DE 39 01167 A1 and EP 1 524 411 B1. It is known especially from the last namedto determine the gap size by means of determining electrical resistancecoefficients in the case of an electrically conducting contact betweenrotor and housing.

Further methods for gap minimization, which, however, are based on thedetection of vibrations in the event of contact between housing androtor, are known for example from GB 2396438A, US 2009/0226302 A1 or US2005/0286995 A1. These methods which are known from the prior art,however, necessitate a high equipment cost or are not very accurate sothat in practice only a displacement of the rotor by a fixed,predetermined length is frequently applied. Therefore, a furtherimprovement with regard to the equipment cost is desired.

SUMMARY OF INVENTION

It is therefore an object of the invention to disclose a method by meansof which the gap between rotor and housing is minimized in a simplemanner at low equipment cost.

The object is achieved according to the invention by an output signal ofa structure-borne sound monitoring system, which is associated with therotor and/or housing, being used as a measure for the size of the gapand therefore for setting a minimum gap, wherein the structure-bornesound monitoring system is a component part of a foreign-body detectionsystem.

The invention is based in this case on the consideration that aparticularly simple monitoring of the gap size would be possible bymeans of sensors which are as non-invasive as possible and are to beattached in the outer regions. A simple signal, which is generated inthe event of contact of rotor and housing, is the sound which ispropagated, moreover, by solid bodies, such as a turbine housing. As aresult, an acoustic detection of vibrations, which are generated byblade tips colliding with the housing, is enabled in the outer regionsof the housing. Therefore, a structure-borne sound monitoring systemallows a particularly simple and technically inexpensive checking of apossible contact of blade tips and housing during a displacement ofhousing and rotor in relation to each other. This enables an accuratesetting of a minimum gap.

According to the invention, the structure-borne sound monitoring systemis a component part of a foreign-body detection system, especially ofthe turbine. Foreign-body detection systems are frequently used inturbines in order to detect in good time possibly penetrating foreignbodies or breaking-away parts of the turbine itself and to initiate ashutdown of the turbine.

Foreign-body detection systems are based on acoustic detection.Therefore, it is advantageous to also use the structure-borne soundmonitoring system of the foreign-body detection system in the manner ofa dual-use system for setting a minimum gap. It may be the case that noconstructional interventions at all in the turbine are even necessaryfor this purpose, but only a corresponding adjustment of sensors andcontrol electrics.

In an advantageous embodiment, the rotor can be displaced in an axialdirection in relation to the housing for adjusting the size of the gap.Owing to the typically conical shape of the turbine, a uniform reductionof the gap over the entire circumference and in each turbine stage isachieved as a result.

The rotor is advantageously displaced just until there is no longer acontact which generates output signals. That is to say, the rotor isdisplaced until the turbine rotor blading comes into contact with thehousing. This contact is monitored by means of a structure-borne soundmonitoring system and as a result of this limits the range of travel. Assoon as a first contact indication is registered, the rotor—after apossibly short reverse displacement—is fixed directly at the limit forcontact.

In a turbine, especially a gas turbine, comprising a rotor, especially arotor blade, and a housing, the gap between rotor and housing isadvantageously minimized by means of the described method.

It is also an object of the invention to disclose a turbine in which thegap between rotor and housing is minimal. This is to be carried out atlow equipment cost.

The object is achieved by a structure-borne sound monitoring systembeing associated with the rotor and/or housing in a turbine and on theoutput side being connected to the adjusting device.

Also with regard to the turbine, the structure-borne sound monitoringsystem is advantageously a component part of a foreign-body detectionsystem and/or the rotor can be advantageously displaced in an axialdirection in relation to the housing for adjusting the size of the gap.

In an advantageous embodiment, the rotor, particularly at the tips ofthe rotor blades, can be at least partially abradable. That is to saythat corresponding abrasion points are provided and are designed for aslight contact of the housing during the adjustment process. At theabrasion points, material is then possibly worn away, but these pointsare designed so that no structural damage to the rotor, especially tothe rotor blades, occurs as a result. Therefore, the rotor can displacedwithout risk up to the point of the slight signal-generating contact,which enables an optimum gap setting.

A power plant advantageously comprises a described turbine.

The advantages which are achieved using the invention are especiallythat by the contact detection between rotor and housing by means of aforeign-body detection system, minimization of the radial gaps is madepossible with technically particularly simple means. The efficiency ofthe turbine is consequently maximized and the power output increased.This also offers advantages with regard to environmental friendlinesssince by means of a control system modification a significant saving infuel and emissions is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail with reference to a drawing.

In this respect, the FIGURE shows a gas turbine.

DETAILED DESCRIPTION OF INVENTION

The FIGURE shows a turbine 100, in this case a gas turbine, in alongitudinal partial section. Inside, the gas turbine 100 has rotor 103which is rotatably mounted around a rotational axis 102 (axialdirection) and which is also referred to as a turbine rotor.

Arranged in series along the rotor 103 are an intake housing 104, acompressor 105, a toroidal combustion chamber 110—especially an annularcombustion chamber 106—with a plurality of coaxially arranged burners107, a turbine 108 and the exhaust gas housing 109.

The annular combustion chamber 106 communicates with an annular hot gaspassage 111. Four series-connected turbine stages 112, for example, formthe turbine 108 there. Each turbine stage 112 is formed from two bladerings. In the hot gas passage 111, a row 125 formed from rotor blades120 follows a stator blade row 115, as seen in the flow direction of aworking medium 113.

The stator blades 130 are fastened on the stator 143 in this case,whereas the rotor blades 120 of a row 125 are attached to the rotor 103by means of a turbine disk 133. The rotor blades 120 therefore formcomponent parts of the rotor or rotating component 103. A generator or aworking machine (not shown) is coupled to the rotor 103.

During operation of the gas turbine 100, air 135 is inducted by thecompressor 105 through the intake housing 104 and compressed. Thecompressed air which is made available at the turbine-side end of thecompressor 105 is directed to the burners 107 and mixed with acombustible medium there. The mixture is then combusted in thecombustion chamber 110, forming a working medium 113. From there, theworking medium 113 flows along the hot gas passage 111 past the statorblades 130 and the rotor blades 120. On the rotor blades 120 the workingmedium 113 is expanded, transmitting an impulse, so that the rotorblades 120 drive the rotor 103 and this drives the working machine whichis coupled to it.

The components which are exposed to the hot working medium 113 aresubjected to thermal loads during operation of the gas turbine 100. Thestator blades 130 and rotor blades 120 of the first turbine stage 112,as seen in the flow direction of the working medium 113, are thermallyloaded most of all next to the heat shield tiles which line thecombustion chamber 106. In order to withstand the temperaturesprevailing there, these are cooled by means of a cooling medium. By thesame token, the blades 120, 130 may have coatings which are resistant tocorrosion (MCrAlX; M=Fe, Co, Ni, rare earths) and to heat (thermalbarrier layer, for example ZrO₂, Y₂O₄—ZrO₂).

The stator blade 130 has a stator blade root (not shown here) whichfaces the inner housing 138 of the turbine 108 and a stator blade tipwhich lies opposite the stator blade root. The stator blade tip facesthe rotor 103 and is fastened on a fastening ring 140 of the stator 143.

On the control system side, the gas turbine 100 has a foreign-bodydetection system which is not shown in more detail according to theFIGURE. This serves for detecting foreign bodies penetrating the gasturbine 100 along with the air 135 or for detecting foreign bodies whichhave broken away due to damage in the turbine 100 and, if necessary, forinitiating a rapid shutdown of the turbine 100. To this end, theforeign-body detection system comprises a structure-borne soundmonitoring system which is connected to a multiplicity of sensors on therotor 103 and housing 138 which emit output signals with regard to theacoustic vibrations which occur in the turbine 100.

Furthermore, the rotor 103 can be axially displaced along the axis 102.On account of the conicity of the tips of the rotor 103 and of thehousing 138 in relation to each other, the gap d between rotor103—especially the rotor blade tips—and the housing 138 is decreased orincreased by an axial displacement of the rotor 103 or of the housing138. The axial displacement is carried out hydraulically.

By an axial displacement of the rotor 103 in relation to the housing138, the existing gap d is made narrower and until finally a firstcontact is made, leading to vibrations and therefore to the creation ofsound. This sound is transmitted by the housing 138 and is detected bythe structure-borne sound monitoring system and converted intocorresponding output signals.

Depending on the axial displacement of the rotor blades 120 in relationto the housing 138, a contact of lesser or greater force is made betweenthe turbine blades 120 and the housing 138, as a result of which thestrength of the generated structure-borne sound, and therefore of theoutput signals, are also changed. In this way, different output signalsare produced as a function of the value of the axial displacement.

If a first contact has been made, the stator blades 120 are fixed or—inthe case of a contact of excessive force—shifted back again just untilthere is no longer a contact indicated by a corresponding output signal.A minimum gap d is then set. This setting of the minimum gap can becarried out during operation of the turbine 100, typically after it haswarmed up.

The turbine blade 120 has an outer wear layer. The outer wear layer isporous and/or ceramic, for example, so that even a slight contact doesnot cause any permanent damage.

1.-10. (canceled)
 11. A method for minimizing the gap between a rotorand a housing, wherein the gap between rotor and housing is adjusted, bydisplacement of the rotor and the housing in relation to each other,wherein an output signal of a structure-borne sound monitoring system,which is associated with the rotor and/or the housing, is used as ameasure for the size of the gap and consequently for the setting of aminimum gap, and wherein the structure-borne sound monitoring system isa component part of a foreign-body detection system of a turbine. 12.The method as claimed in claim 11, in which the rotor is displaced in anaxial direction in relation to the housing for adjusting the size of thegap.
 13. The method as claimed in claim 11, wherein the rotor isdisplaced just until there is no longer a contact between rotor andhousing which generates output signals.
 14. A turbine comprising a rotorand a housing, comprising an adjusting device wherein the gap betweenrotor and housing can be adjusted by means of the adjusting device, bydisplacement of rotor and housing in relation to each other, astructure-borne sound monitoring system associated with the rotor and/orthe housing and on the output side connected to the adjusting device,wherein the structure-borne sound monitoring system is a component partof a foreign-body detection system of a turbine.
 15. The turbine asclaimed in claim 14, in which the rotor can be displaced in an axialdirection in relation to the housing for adjusting the size of the gap.16. The turbine as claimed in claim 14, in which the rotor is at leastpartially abradable.
 17. A power plant with a turbine as claimed inclaim 14.